1. Field of the Invention
This invention relates to a waveform measuring apparatus and, more particularly, to a waveform measuring apparatus with a marker zone displaying function, which includes a signal analyzer such as a spectrum analyzer (including an optical spectrum analyzer), a network analyzer, or the like.
Also, this invention relates to a waveform measuring apparatus such as a spectrum analyzer for analyzing a signal and displaying a waveform such as a spectrum. Of waveforms such as spectra displayed on a display screen, a desired waveform zone is quickly selected, and specific characteristic values such as a maximum level and a corresponding frequency within the selected zone are detected and displayed.
2. Description of the Related Art
When a spectrum of an unknown signal is analyzed and evaluated, the level and frequency of the spectrum of interest must be detected first.
However, in practice, elements constituting the spectrum analyzer have a limited resolution, and the waveform of the spectrum of interest is not displayed by a single line. That is, the upper portion of the spectrum is represented by a moderate curve and the lower portion thereof has an inverted V-shape, with variations depending on measurement conditions. The level and frequency of the maximum level point of the inverted V-shaped spectrum display correspond to the level and frequency of the spectrum of interest. Thus, the maximum point of the spectrum must be searched. Many spectra are present in neighboring frequency regions. For this reason, in order to measure the levels and frequencies of these spectra, each spectrum must be selected, and the maximum level point of each spectrum on the display screen must be detected. In some cases, the spectrum may be displayed in a V shape. In this case, the level and frequency of the minimum level point correspond to those of the spectrum of interest. In the following description, a case will be described wherein an inverted V-shaped spectrum is displayed. The related arts associated with a method of displaying a spectrum and its maximum level and frequency will be described below.
The first related art is a digital storage type spectrum analyzer which stores level data of a spectrum in correspondence with a frequency, and then displays the data on a display screen. In this analyzer, a spot is set at a desired position of a spectrum waveform on the display screen. A frequency is detected based on the position of the spot on the frequency axis, and the level corresponding to the frequency indicated by the spot is detected from the memory, thereby displaying these values.
The second related art is a so-called peak search function and a next peak search function performed in a digital spectrum analyzer having a memory as in the first related art. In the peak search function, a maximum level is searched from level data stored in the memory, and a frequency corresponding to the maximum level is detected and displayed. A spot is set at a position corresponding to the maximum level point in the entire frequency region on the display screen.
In the next peak search function, the second highest level point in the frequency region on the display screen, i.e., the second highest spectrum level and its frequency are detected.
The third related art is an analog spectrum analyzer which analog-displays level data of a spectrum without using the above-mentioned memory. In this spectrum analyzer, a desired frequency range and position are set on the spectrum waveform on the display screen to be visually observed, and the maximum level within the frequency range is held in an analog manner, thereby displaying its maximum level.
The above related arts have the following drawbacks.
The first related art is convenient for detecting a level and frequency at a desired point on a spectrum of interest on the display screen. However, in order to accurately set the spot at the maximum point of the spectrum, the spot must be moved and this operation is time-consuming. In a digital display, if a design is made to improve a resolution along the frequency axis in order to allow visual observation of a displayed image in an analog manner, the setting resolution of the spot is improved accordingly and accuracy is also improved. However, a distance for moving the spot from the left to the right end of the display screen is prolonged, and setting of the spot takes much time. A signal for setting the position of the spot is manually generated, and it must be visually confirmed whether or not the spot is set. Since the setting of the spot must be visually confirmed, a delay time or inertia is generated due to a transient response of a circuit present between a manual operation and setting of a spot on the display screen, and manual operation cannot be synchronized with from visual confirmation. Therefore, it is difficult to quickly set a spot at a desired position, and this operation is time-consuming. When the spectrum display on the display screen has a inverted V-shape, it is difficult to find the maximum level point unless the maximum level point is determined after a portion regarded as a maximum level point is searched once using the spot. In this method, if the frequency of the unknown signal to be observed varies, the position of the spot is also offset from the maximum level point. Therefore, the position of the spot must be reset.
In the second related art, when many spectra are displayed on the display screen, a level and frequency of a desired spectrum, in particular, a spectrum having a lower level, cannot be detected. In the peak search function, even if the frequency of a signal to be measured is varied, the spot can follow the variation without being offset from the maximum level point as long as the frequency falls within the entire frequency region on the display screen. However, in the next peak search function, if the frequency and/or level of each spectrum is changed, it is difficult to accurately detect it.
In the third related art, a maximum level in a given frequency range of a spectrum on the display screen is displayed. However, the frequency of the spectrum cannot b detected and displayed. Since the peak hold circuit is realized by an analog circuit, this circuit cannot be operated in correspondence with frequencies. Therefore, when the maximum level is detected, it is difficult to specify the frequency of the level.
The drawbacks of the related arts are as described above.
These drawbacks are also presented when waveforms including wavelengths and physical characteristics are displayed, as well as a case wherein a spectrum is displayed.